[3-155] – (Chain) from Abu Abdullah (alaihi salam), which said about words of Allah- : And when the female infant buried alive is asked * For what sin she was killed, – this was revealed about Husayn ibn Ali – alaihuma salam.

I do believe that you are more honest than other shias, so you have to mention that your opinion on maraseel of ibn Abu Umayr is only one opinion, and there is a second one. Which is also popular in shia world and accepted by many classical shia scholars. And in accordance to them this report would be sound.

Jafar Subhani in “Kulliyat fi Ilmul Rijal” p 21, quoted al-Hilli, which after quotation of mursal by ibn Abu Umayr, said:
وعلى هذه عمل الأصحاب ولا طعن في هذه بطريق الإرسال ، لعمل الأصحاب بمراسيل ابن أبي عمير
And upon this acted (our) companions, and there is no room to reject this way (of transmission) due to disconnection, due to action of (our) companions by maraseel of ibn Abu Umayr”

And he also quoted there al-Fadl Abi, and he is Hasan ibn Abi Talib, known as Abi Tarat, which said after mentioned mursal of ibn Abu Umayr:
وهذه وان كانت مرسلة ، لكن الأصحاب تعمل بمراسيل ابن ابي عمير ، قالوا : لانه لا ينقل إلا معتمداً
And this is even if it is disconnected, but companions acted upon maraseel of ibn Abu Umayr, they said: he didn’t transmitted except what was reliable.